Self-assembly of octanethiol on oxide-free cobalt electrode from aqueous solution under electrochemical control

Abstract

Self-assembly of alkanethiols on Co surface from organic solution has met with limited success due to the presence of the native oxides. A way needs to be found to remove any oxide and form perfect self-assembled monolayers (SAMs). We report the development of electrochemical approach for formation of alkanethiol self-assembled monolayers on base metals in aqueous solutions. For formation of octanethiol (OT) SAMs on oxide-free cobalt surfaces, we combine the surface renewal technique with in situ electrochemical procedure of removing the native oxide, thiol adsorption, and electrochemical control of SAMs properties in one aqueous solution. The use of aqueous thiol-containing media results in removing any oxide by electrochemical reduction, accelerated monolayer formation under electrochemical control, and investigating SAMs surface coverage and monolayer integrity by voltammetry. In this work, we study the influence of different factors on self-assembly process such as the surface pretreatment, adsorption time, the presence of dissolved oxygen, solution pH, and potential cycling on polycrystalline cobalt microelectrode from aqueous 0.1 M NaClO4 solutions of 0.1 mM OT. We obtain the high-quality self-assembled monolayers which are stable in wide range of potentials and show blocking characteristics toward the following Faradaic processes: Co surface oxidation and O2 and H+ reduction.